I'm thinking of backing up important CDs and DVDs by not simply copy-pasting the files from the CD or DVD, that's why i'd like to create ISO image files instead. What's a good app for that? It should run smoothly on Fedora 11.

This question appears to be off-topic. The users who voted to close gave this specific reason:

"Questions seeking product, service, or learning material recommendations are off-topic because they become outdated quickly and attract opinion-based answers. Instead, describe your situation and the specific problem you're trying to solve. Share your research. Here are a few suggestions on how to properly ask this type of question." – a CVn, mpy, Tog, Kevin Panko, Scott

The above Gnome steps are really only valid for Gnome 2.
As @cept0 pointed out, this doesn't work for Fedora 20, which uses Gnome 3. A default fedora through Fedora 14 could use the above Gnome steps. The following will work on Fedora 19 & 20 for sure, Fedora 15 -18, you're on your own ;)

In Gnome 3 you can :

Insert the CD (or DVD) into the drive.

Run the gnome-disk-utility. Several ways to do this. Typing "disc" or "iso" in the activities search area will work.

Click on the gear in the upper right corner

In the drop down select "Create Disk Image"

Change the name & save location if you like and select "Start Creating"

Gnome's nautilus, as DaveParillo suggests, uses Brasero, so if you're not using Gnome, just install Brasero (in Fedora it's a standard package, you might already have it---don't know about other distros), then choose "Copy CD/DVD", and do as Dave says.